Many conferencing systems implement a “front-end” ingress service with a voice user interface (VUI) that users dial into. The VUI typically implements an interactive voice response (IVR) system that is used to identify the meeting (e.g., meeting ID), the user (i.e., conference participant), solicit authentication and/or credential information from the user, and then handoff (i.e., transfer) the user to a specific instance “back-end” conference service. The specific conference service is responsible for allocating necessary resources and establishing the connections/media paths required to actually conduct and manage the conference session. When the conference service is co-located with the VUI, the handoff from the front-end service to the back-end service is a relatively simple internal operation, requiring little or no protocol interaction with the user's endpoint device. Often times, however, the front-end and one or more back-end services are split due to reasons that include the need for the scheduling system to distribute the load on various network resources. When the conference or meeting is handled by a different service on a separate network server from the VUI, a need arises for a protocol that causes the endpoint dialog with the front-end VUI service to re-target to the back-end conference service without a new call being placed.
One prior art method for implementing the handoff from the VUI to the conference service utilizes a basic Session Initiation Protocol (SIP) REFER message that is sent from the VUI server to the user endpoint device. SIP is a well known protocol used for setting up and tearing down voice, video, or other multimedia calls. The actual multimedia communications in SIP is done, for example, using the Real-Time Transport Protocol (RTP). SIP is one of the leading signaling protocols for voice over IP (VoIP) communications. The SIP REFER method is documented in Request for Comments (RFC) 3515. The SIP REFER sent from the VUI causes the endpoint to send a new INVITE message to the proper conference server. One problem with this approach, however, is that it typically lacks a security mechanism for properly authenticating the endpoint device with the conference service. For example, if the VUI server is responsible for collecting and verifying authentication and authorization information from the user endpoint device, a secure method for conveying information that the authorization was successful must be included in the REFER to the endpoint, and the endpoint must be able to further convey that information in the INVITE to the conference server in a secure fashion. Some endpoints may be unable to provide such a secure conveyance.